Diesel cylinder lubricant oil composition

ABSTRACT

Provided are formulations, methods of making, and methods of using a diesel cylinder lubricating oil composition to achieve enhanced corrosive wear control on the cylinders of a 2-stroke diesel engine, wherein such lubricating oil composition comprises, among other things, an amount of one or more surfactant materials sufficient to provide substantially improved capacity to reduce or inhibit corrosive wear.

The present invention relates to lubricant oil compositions suitable foruse in two-stroke diesel engines. In particular, the present inventionrelates to diesel cylinder lubricant oil compositions. Moreparticularly, the lubricant oil compositions of the present inventionmay be used to lubricate the power cylinders in diesel engines burningfuels that have conventional sulfur levels or those that have lowersulfur levels. Each of the diesel cylinder lubricant oil compositions ofthe present invention comprises, inter alia, one or more surfactantmaterials that impart improved capacity to control the corrosive-wear onthe power cylinders. Moreover, the corrosive wear-controlling surfactantmaterials of the present invention are compatible with conventionaldiesel cylinder lubricant oils that have total base numbers (“TBN”) ofat or above 70 (“high TBN oils”). These surfactant materials are alsocompatible with diesel cylinder lubricant oils of lower TBNs, which mayin turn be preferably used to lubricate engines powered by fuels thatcontain lower-than-conventional levels of sulfur. Furthermore, thepresent invention is concerned with methods of providing enhancedprotection against corrosive wear, while preventing excessive depositbuildups, and providing lubrication to the cylinders in 2-stroke dieselengines. The present invention also relates to the methods of preparingsuch diesel cylinder lubricant oil compositions.

In the not so distant past, rapidly escalating energy costs,particularly those incurred in distilling crude oil and liquidpetroleum, became burdensome to the users of transportation fuels, suchas owners and operators of seagoing ships. In response, those users havesteered their operations away from steam turbine propulsion units infavor of large marine diesel engines that are more fuel efficient.Diesel engines may generally be classified as slow-speed, medium-speed,or high-speed engines, with the slow-speed variety being used for thelargest, deep shaft marine vessels and certain other industrialapplications. Slow-speed diesel engines are unique in size and method ofoperation. The engines themselves are massive, the larger units mayapproach 200 tons in weight and an upward of 10 feet in length and 45feet in height. The output of these engines can reach as high as 50,000brake horsepower with engine revolutions of more than 100 revolutionsper minute. They are typically of crosshead design and operate on thetwo-stroke cycle. Medium-speed engines, on the other hand, typicallyoperate in the range of about 250 to about 1100 rpm and may operate oneither the four-stroke or the two-stroke cycle. These engines can be oftrunk piston design or occasionally of crosshead design. They typicallyoperate on residual fuels, just like the slow-speed diesel engines, butsome may also operate on distillate fuels that contain little or noresidue. These engines can also be used for propulsion, ancillaryapplications or both on deep-sea vessels. Slow- and medium-speed dieselengines are also extensively used in power plant operations. Thelubricant oil compositions and methods of the present invention areapplicable to those operations as well.

A slow- or medium-speed diesel engine that operates on the 2-strokecycle is typically a direct-coupled and direct-reversing engine ofcrosshead construction, with a diaphragm and one or more stuffing boxesseparating the power cylinders from the crankcase to prevent combustionproducts from entering the crankcase and mixing with the crankcase oil.The notable complete separation of the crankcase from the combustionzone has led persons skilled in the art to lubricate the combustionchamber and the crankcase with different lubricating oils. The corrosivewear-controlling surfactant materials and lubricant oil compositions ofthe present invention may be advantageously applied to lubricate thepower cylinders of these diesel engines, although there is no reason tobelieve that these additives or compositions, with slight modificationof low-temperature properties such as viscosity, would not be suitablefor lubricating the crankcases as well.

Traditionally, fuels used for diesel engines have a high sulfur contentof at least 3.5%, and typically of at least 4.5%. The high sulfur levelsin diesel fuels has led to the generation and release of large amountsof sulfur oxides (SO_(x)) in the exhaust gases. Aside from polluting theair, the sulfur oxides react with the moisture that is also present inthe exhaust gases to form sulfuric acid, which in turn corrodes theengine. To combat acidic corrosion, persons skilled in the art haveformulated diesel cylinder lubricant compositions to include variousoverbased metallic detergents, which are capable of neutralizing thesulfuric acid. For example, conventional marine diesel cylinderlubricant compositions typically have a total base number (“TBN”) of atleast 70 (as determined using ASTM D2896). Those conventional dieselcylinder lubricant compositions are referred to as “high TBN oils”herein.

In recent years, legislations in various countries and regions of theworld sought to reduce pollution from diesel engines of ships and otherindustrial applications by including measures to reduce the amount ofsulfur in marine fuels. For example, the International MaritimeOrganization's MARPOL Annex VI “Regulations for the Prevention of AirPollution from Ships” has imposed stricter pollution regulations,including limits on sulfur oxide. In some geographic areas, often called“SO_(x) Emission Control Areas,” or “SECAs,” restrictions on sulfur infuel are particularly stringent. Those areas include, for example, theBaltic Sea and the North Sea. Some regulations have already beenimplemented while others are promulgated but awaiting implementation.For example, in May of 2005, a cap of 4.5% sulfur in diesel fuel wasimposed globally. In May of 2006, a cap of 1.5% sulfur was imposed inthe Baltic Sea. In August 2007, a cap of 1.5% sulfur will be imposed inthe North Sea.

As a result of the gradual implementation of these regulations, thelevels of sulfur in diesel fuels vary currently depending on thecountries and/or regions. Accordingly, an oceangoing vessel may berequired to use diesel fuels having a level of sulfur below 1.5% in someparts of the world, but as it navigates to some other areas, be requiredto use diesel fuels having a level of sulfur as high as 4.5%. Certaindiesel cylinder lubricant oils have been formulated specifically for theSECAs where the sulfur levels in diesel fuels are below 1.5%. Theselubricant oils are called “low TBN oils,” because they typically have aTBN of at or below 40. Operators of stationary diesel engines in theSECAs as well as ship owners who operate exclusively or primarily inthose areas also have the option to continue to use the conventionalhigh TBN oils (i.e., lubricant oils with a TBN of at or above 70), butthey must apply those oils at a slower feed rate to avoid producingexcessive hard deposits on the cylinders due to high thermal loads onunreacted neutralizing additives. This approach, though theoreticallyfeasible, is often prohibitively cumbersome in practice, because itrequires that the operator of the diesel engines monitor the cylinderscontinuously and adjust the feed rate according to the levels ofdeposits and wear he observes. This reduction and continued adjustmentof feed rate is necessary to prevent not only the excess hard deposits,but also the loss of controlled corrosion when a high TBN oil is used ina low sulfur environment. The excess hard deposits would otherwise formprimarily on the crown land and impact the oil film, leading to scuffingand ultimately to deposits behind the rings and the ring grooves. A highTBN oil applied at its usual feed rate in a low-sulfur environment willreduce corrosion so much that the liner surfaces become too smooth andunable to hold the lubricant oil. This over-reduction of corrosion isalso known as “lack of controlled corrosion,” and will in turn lead towear and continued polishing of the liner's surface. Scuffing as aresult of direct metal-to-metal contact is inevitable in a prolongedabsence of controlled corrosion. Thus, prudent users of diesel engineswho operate exclusively or primarily in the SECAs typically switchentirely to low TBN oils for their lubrication needs rather thanundertake the delicate task of continuously adjusting the feed rate ofhigh TBN oils in accordance with the changing engine conditions.

Majority of the world's deep sea fleet, however, is represented by shipsthat operate only part time in the SECAs. These ships typically traveland/or operate at sea for weeks if not months at a time, therefore, mustcarry lubricants onboard to replenish or replace used oils, so thattheir engines are effectively lubricated and protected from the perilsof harsh operating conditions. While it is possible for an owner oroperator of such a ship to carry onboard only a high TEN oil, using itat the full feed rate in the non-SECAs and at reduced feed rate in theSECAs, the exacting requirement of monitoring the power cylinders andadjusting the feed rate according to the levels of hard deposits makesthis approach disagreeable. It is also a risky approach. Under certaincircumstances where very low sulfur diesel fuels must be used, the feedrates may need to be so low that substantial engine wear may occur. Ithas thus become the preferred approach for ship owners or operators tocarry onboard both a high TBN oil and a low TBN oil, so that a choicebetween those two oils can be made depending on the levels of sulfur inthe available diesel fuels.

In the long term, all areas or regions of the world will likely berequiring low-sulfur diesel fuels. In the near future, however, shipowners or operators would continue to carry both a low TBN and high TENcylinder lubricant oil onboard their vessels. An alternative, or perhapsmore preferred, approach may be to carry various additives onboard shipsas oil-concentrates so that lubricants can be blended in situ accordingto both the diesel fuel types and the conditions (e.g., levels of wearand deposits) of the cylinders. The present invention pertains tocertain corrosive wear-control surfactant materials that can be madeinto oil concentrates and serve this purpose competently. Thoseadditives are compatible with both high TBN and low TBN oils, thus canbe blended into the lubricant oils for applications in both the SECAsand the non-SECAs.

Corrosive wear is a well-known problem in diesel engines. This type ofwear distinguishes from physical wear or scuffing caused by directcontact of moving metal surfaces. To combat stuffing or physical wear,persons skilled in the art typically use friction modifiers, which areknown to simply reduce the friction between surfaces that come intocontact with each other during operation, thus reducing wear to thesesurfaces. Specifically, as the surfaces move closer together, thelubricant is squeezed out between them. During this process, thefriction modifier molecules in the lubricant become adsorbed onto thesurfaces, thereby retained between the surfaces, displaying a molecularorientation perpendicular to the surfaces, reducing the level of contactand lowering the friction.

As illustrated above, there is a limit to how much one might increasethe TBN of a given lubricant oil, even though it might theoretically bepossible to neutralize all of the sulfuric acid produced duringcombustion, because of concerns for hard deposits and loss of controllederosion. As a result, persons skilled in the art use certain otheradditives to supplement corrosive wear control. Examples of suchadditives include various zinc-containing compounds. For example, U.S.Pat. No. 4,842,755 disclosed a marine diesel cylinder lubricant having abase number of at least 60. The composition includes a borated ashlessdispersant, one or more overbased metal compounds and a zinc dialkyldithiophosphate providing 0.02 to 0.23 wt. % (200 to 230 ppm) of zinc.Notably, increasing the amount of zinc above about 230 ppm unexpectedlyled to a loss of performance benefits in ring and linear wear. U.S. Pat.No. 4,948,522 disclosed marine diesel cylinder lubricants comprising aborated dispersant and a polybutene, and optionally a zincdialkyldithiophosphate and/or overbased metal detergent. Thoselubricants were said to have improved ring wear and liner wearperformance and good protection against corrosion. U.S. Pat. No.6,140,280 disclosed succinimide compounds that exhibit corrosionresistance and wear resistance in diesel engines. It also disclosed thatconventional anti-wear agents such as zinc dithiophosphates andmolybdenum dithiocarbamates, may be used as co-additives to boostresistance to corrosive wear.

With the development of low TBN lubricant oils, the need for corrosivewear control becomes more acute. Even with the low sulfur levels in thefuels, the parts in the diesel engines remain exposed to sulfuric acidin the exhaust. At such low TBN levels, the sulfuric acid producedduring combustion are typically not effectively neutralized. Certainadditives have been found to enhanced corrosive wear control in a lowTBN environment. For example, in U.S. patent application Ser. No.10/947,093 (published as US 2005/0153847 A1, on Jul. 14, 2005), a marinediesel cylinder lubricant composition having a total base number of atleast 30, preferably at least 35 or more, comprising (a) at 40 wt. % ofan oil of lubricating viscosity; (b) at least one detergent preparedfrom at least two surfactants, preferably phenate and sulfonatesurfactants; (c) at least one boron-containing dispersant providing atleast 100 ppm of boron; and (d) at least one zinc-containing antiwearadditive preferably a zinc dihydrocarbyl dithiophosphate providing morethan 230 ppm, preferably at least 250 ppm, of zinc. That lubricantcomposition was said to provide improved protection against corrosivewear in the presence of 230 ppm of zinc, and was said to provide goodwear protection even at a low total base number, such as for example,when used in a high sulfur environment. U.S. patent application Ser. No.11/265,838 (published as US 2006/0116298 A1 on Jun. 1, 2006), discloseda lubricant oil composition that purportedly offered effective cylinderliner protection, particularly in the areas of the cylinder that areprone to corrosive wear. That composition comprised (a) a major amountof oil of lubricating viscosity; and (b) a minor amount of anoil-soluble or oil-dispersible molybdenum compound, and had a TBN offrom 20 to 100 and a viscosity at 100° C. in the range of from 9 to 30mm² s⁻¹.

We have found surprisingly that certain surfactant materials, whenincluded in a lubricating oil composition for 2-stroke diesel enginecylinders, substantially enhance the capacity of the oil to preventcorrosive wear on those cylinders. Moreover, their capacity to controlcorrosive wear is not affected by the TBN of the lubricant oilcomposition. Furthermore, these surfactant materials provide enhancedcorrosive wear control without adding to the extent of overbasing in thelubricant oil, making them particularly suitable for use as additives inlow TBN oils. Those additives are divergent in their mechanisms ofaction, although all can be categorized structurally as surfactants orsurfactant-related materials.

This finding offers new possibilities for controlling corrosive wear in2-stroke diesel engines, especially those that drive seagoing vesselsoperating in both low and high sulfur fuel regions. The surfactantmaterials of the invention offer particular advantages if an owner oroperator of a vessel opts to take various lubricant additives onboard asoil concentrates, blending them into lubricant oils that would suit thereal-time lubrication needs. The finding of these materials allows theowner/operator to carry on board a single type of corrosive-wearinhibitor that can be blended into low TBN oils, high TBN oils, and oilsthat have intermediate TBNs as a result of mixing various proportions oflow TBN oils and high TBN oils. Furthermore, because at least some ofthese additives are equally known to provide dispersancy, their oilconcentrates can serve multiple purposes, further reducing the number ofadditives that must be carried onboard seagoing vessels.

The present invention thus provides 2-stroke diesel cylinder lubricantcompositions comprising various oil-soluble surfactant materials thatdemonstrate enhanced protection against corrosive wear. The term“oil-soluble” as used herein refers to compounds that are soluble undernormal blending conditions in the base stocks or in an additive package.The present invention further provides methods for preparing thesediesel cylinder lubricant compositions and using them to preventcorrosive wear of power cylinders in 2-stroke diesel engines. Moreover,the present invention provides methods of blending an oil-concentrate ofthese surfactants in situ with one or more other suitable componentsinto diesel cylinder lubricant compositions, and using such blendedcompositions to lubricate and protect 2-stroke diesel engines fromcorrosive wear.

SUMMARY

It has been found that the inclusion of one or more surfactant materialsin certain 2-stroke diesel cylinder lubricant compositions improves theability of the lubricant compositions to protect the power cylindersfrom corrosive wear. This protection has been observed regardless ofwhether the diesel engine at issue burns a high-sulfur heavy diesel fueloil (i.e., having a sulfur level of about 1.5% to about 4.5%) or alow-sulfur heavy diesel fuel oil (i.e., having sulfur level of at orbelow about 1.5%). One or more surfactant materials of the presentinvention can be blended into a diesel cylinder lubricant compositionbefore the composition is loaded onboard seagoing vessels, but may alsobe carried onboard as an oil-concentrate, to be blended in situaccording to the real-time lubrication needs and fuel types.

The first aspect of the present invention pertains to a corrosive-wearreducing and/or inhibiting oil-soluble surfactant material suitable asan additive to a diesel cylinder lubricant oil composition. Theadditive's ability to control corrosive wear is not the result of highTBN. Nor is it affected by the TBN of the lubricant oil composition towhich the inhibitor is a part. The diesel cylinder lubricant oilcomposition of this aspect can be used to lubricate the cylinders of a2-stroke diesel engine that burns heavy diesel fuels containing as lowas less than about 1.5% and/or as high as about 4.5% of sulfur. Theadditive of this aspect may also be in an oil concentrate form.

The second aspect of the present invention pertains to a diesel cylinderlubricant composition with improved corrosive wear control propertiescomprising a corrosive wear inhibitor of the first aspect. The dieselcylinder lubricant composition of this aspect can be used to lubricatethe cylinders of 2-stroke diesel engines burning any currently availablediesel fuels.

This invention, in its third aspect, provides a method of making adiesel cylinder lubricant composition of the second aspect. In thisaspect, the invention also provides a method of blending a dieselcylinder lubricant composition of the second aspect onboard a sea-goingvessel using an oil-concentrate of a corrosive-wear inhibitor of thefirst aspect, the amount of which depending on the real-time lubricationneeds and/or the extent of wear of the particular cylinders to belubricated.

In its fourth aspect, this invention pertains to a method of providingand maintaining optimal levels of protection for the cylinders of a2-stroke diesel engine against corrosive wear by applying a lubricantcomposition of the second aspect.

Persons skilled in the art will understand other and further objects,advantages, and features of the present invention by reference to thefollowing description.

DETAILED DESCRIPTION OF THE INVENTION

Various preferred features and embodiments are described below by way ofnon-limiting illustrations.

1. Surfactant Materials

The present invention relates to a lubricant oil composition suitablefor reducing and/or inhibiting corrosive wear on the power cylinders of2-stroke diesel engines, comprising one or more certain oil-solublesurfactant materials. Specifically, the oil-soluble surfactants of thepresent invention are molecules that have traditionally been associatedwith deposit control or dispersancy, but are not known to controlcorrosive-wear. Moreover, the surfactant materials of the presentinvention can be carried on board seagoing vessels as an integral (i.e.,blended) part of a marine cylinder lubricant, or as an oil concentratethat is later blended in situ depending on the contemporaneous sulfurlevels of the diesel fuels, the particular lubrication needs of the2-stroke diesel engines, and the extent of wear on the cylinders.Furthermore, the surfactant materials of the present invention, whenincorporated in a sufficient amount into either a high TBN oil or a lowTBN oil, can effectively reduce corrosive wear on the cylinders of2-stroke diesel engines regardless of the sulfur levels in the fuelsthat drive those engines. Aside from reducing or inhibiting corrosivewear, some of these oil-soluble surfactant materials retain theirtraditional capacity to provide dispersancy, therefore allowing theiruse as multi-functional additives.

As used herein, the term “surfactant material” refers to a molecule thathave surfactant properties and can be classified a surfactant. It alsorefers to a molecule that is derived from such a surfactant, which isnot so substantially changed from the surfactant precursor as to losethe surfactant characteristics. As it is understood by those skilled inthe art, a surfactant is a material that can reduce the surface tensionof water by at least 5%, or at least 10%, or at least 20%, or at least30%, or at least 40%, when used in even small amounts.

A surfactant molecule typically comprises a hydrophobic end and ahydrophilic end. The hydrophobic end of a surfactant molecule isgenerally about 8 to about 20 carbon atoms long. This end can bealiphatic, aromatic, or a mixture of both. The sources from which thehydrophobic end of the molecule may be derived include, for example,natural fats and/or oils, petroleum fractions, relatively shortsynthetic polymers, or relatively high molecular weight syntheticalcohols.

While the hydrophobic end of a surfactant is important, persons skilledin the art typically classify each surfactant based on its hydrophilicend. There are four classes of surfactants: (1) anionic surfactants; (2)cationic surfactants; (3) non-ionic surfactants; and (4) zwitterionicsurfactants. In an anionic surfactant, the hydrophilic end comprises ananionic group. Anionic hydrophophilic groups may be, for example,carboxylates, sulfates, sulfonates, and phosphates. Accordingly, anionicsurfactants may be, for example, sodium dodecyl sulfate (SDS), ammoniumlauryl sulfate, and other alkyl sulfate salts; sodium laureth sulfate,also known as sodium lauryl ether sulfate (SLES); alkyl benzenesulfonate; and fatty acid salts. In a cationic surfactant, thehydrophilic end comprises a cationic group. Cationic hydrophilic groupsare most often derived from a quaternary ammonium cation of thestructure NR₄ ⁺ with the R's being alkyl groups. Examples of cationicsurfactants include cetyl trimethylammonium bromide (CTAB), also knownas hexadecyl trimethyl ammonium bromide; other alkyltrimethylammoniumsalts; cetylpyridinium chloride (CPC); polyethoxylated tallow amine(POEA); benzalkonium chloride (BAC); and beazethonium chloride (BZT). Ina non-ionic surfactant, the non-ionic hydrophilic group is typicallyassociated with water at the ether oxygens of a polyethylene glycolchain. Non-ionic surfactants may be, for example, alkyl poly(ethyleneoxide); alkyl polyglucosides, such as octyl glucoside and decylmaltoside; various fatty alcohols, such as cetyl alcohol and oleylalcohol; various cocamide derivatives that can be prepared from fattyacids of coconut oils, such as cocamide MEA, cocamide DEA, and cocamideTEA. A surfactant may also contain two oppositely charged groups on oneor more of hydrophilic ends. In that case, the surfactant is azwitterionic surfactant. A zwitterionic surfactant molecule iselectrically neutral when it is at the isoelectric point. Zwitterionicsurfactants may be, for example, dodecyl betaine; dodecyl dimethylamineoxide; cocamidopropyl betaine; and coco ampho glycinate. Regardless thetype, surfactant molecules form clusters in water when present in aconcentration higher than a certain threshold. In those clusters, thehydrophilic ends of the molecules line up on the outside of the cluster,facing the water, while the hydrophilic ends of the molecules pointinward. If the surfactant molecules are present in an oil, then areverse cluster may form, with the hydrophobic ends of the moleculespointing outward towards the oil and the hydrophilic ends pointinginward. These clusters are called micelles, and they are typicallyformed when the concentration of the surfactants reaches a certainthreshold. Such a threshold is in turn called “critical micelleconcentration.”

Certain of the surfactant materials of the present invention may havecharacteristics of detergents. Unlike detergents typically used asadditives to diesel cylinder lubricant oils, however, the surfactantmaterials of the present invention are generally not overbased or onlyvery slightly overbased. The TBN of a suitable surfactant molecule istypically at or below about 50, such as below about 20, preferably fromabout 0 to about 17. As conventionally defined, the degree of overbasingis the number of equivalents of the metal base per equivalent of theacid substrate. The total base number, or TBN, of a given moleculereflects its ability to neutralize acids. Typically, a molecule is saidto be non-overbased when it has a TBN of about 0. A low overbasedmolecule has a TBN of above 0 but below about 60. A highly overbasedmolecule has a TBN of about 60 to as high as about 500.

In an exemplary embodiment of the present invention, a sulfonatesurfactant material that may also be characterized as a detergent isadded to a diesel cylinder lubricant oil composition to provide enhancedcorrosive wear control, but the TBN of the lubricant oil is primarilyprovided for by a pair of other highly overbased, detergents. In thatembodiment, then, the overbasing in the detergents provides theacid-neutralizing capacity to the lubricant oil composition, while thesurfactant of the present invention provides the enhanced corrosive wearcontrol. Typically, a surfactant material of the present inventioncontributes less than about 10%, more preferably, less than about 5%, orless than about 2%, of the TBN to the lubricating oil composition towhich it is a part.

Certain other suitable surfactant materials of the present invention mayhave characteristics of dispersants. Accordingly, that surfactantmaterial may serve in dual capacity as a dispersant and a corrosive-wearinhibitor in the diesel cylinder lubricant oil composition to which itis a part. In that case, the surfactant material of the presentinvention is generally metal-free and thus does not lead to ashformation. In addition to preventing or reducing corrosive wear on thepower cylinders, that surfactant material also serves to suspenddeposits or precursors of deposits in oil. That surfactant material maysuspend deposits or precursors of deposits by, for example, includingthe undesirable polar species into micelles; associating with colloidalparticles, thereby preventing them from aggregating and falling out ofsolution; suspending aggregates after they are formed in the bulklubricant; modifying soot particles to prevent aggregation; or loweringthe surface/interfacial energy of the polar species to prevent theiradherence to metal surfaces.

A diesel cylinder lubricant oil composition of the present inventioncomprises one or more surfactant materials as described above. The oneor more surfactant materials are suitably present in the lubricant oilcomposition in an amount sufficient to offer substantially improvedcapacity to inhibit or reduce the corrosive wear. The term “inhibit orreduce” as used herein, refers to a reduction in corrosive wear that ismeasurable in a properly designed bench or engine test mimicking theconditions under which a 2-stroke diesel engine typically operate. Anexample of such an engine test is the Bolnes Engine Test, as describedin various recent U.S. patent applications, including, for example, U.S.patent application Ser. No. 10/481,486 (published as US 2004/0235684 A1on Nov. 25, 2004), and U.S. patent application Ser. No. 10/947,093(published as US 2005/0153847 A1 on Jul. 14, 2005). Disclosures of theseapplications, to the extent they are relevant to the Bolnes Engine Test,and to the extent they do not conflict with the disclosures and claimsherein, are incorporated by reference. An example of an art-acceptedbench test is the Falex™ Pin and Vee-Block Method, as described, forexample, on page 393 of the FUELS AND LUBRICANTS HANDBOOK: TECHNOLOGY,PROPERTIES, PERFORMANCE, AND TESTING (Totten ed. ASTM International,West Conshohocken, Pa. 2003). The term “substantially improved” as usedherein refers to improvements that are at least 2%, or at least 5%, oreven at least 10%, as compared to the results generated by a samplecontaining no such surfactant material.

Advantageously, the one or more surfactant materials of the presentinvention may be present in the diesel cylinder lubricant oilcomposition in an amount of about 2 wt. % to about 25 wt. %. Preferably,however, the one or more surfactant materials may be present in thediesel cylinder lubricant oil in an amount of about 4 wt. % to about 20wt. %, or about 5% to about 15 wt. %. In an exemplary embodiment of thepresent invention, the surfactant material employed to inhibit or reducecorrosive wear in a diesel cylinder lubricating oil is a mixture of C₁₈to C₂₈, linear alkyl phenol isomers present in an amount of about 7 wt.%, based on the total weight of the lubricating oil composition. Inanother exemplary embodiment of the present invention, the surfactantmaterial employed is a low-overbased (having a TBN of about 17) calciumsulfonate, present in an amount of about 8 wt. %, based on the totalweight of the lubricating oil composition.

2. Oil of Lubricating Viscosity

The oil of lubricating viscosity may be any oil suitable for thelubrication of large diesel engines including, for example, cross-headengines or trunk piston engines. The lubricating oil may suitably be ananimal, a vegetable or a mineral oil. The lubricating oil may further bea petroleum-derived lubricating oil such as, for example, anaphthenic-base, paraffinic-base, or mixed-base oil. Alternatively thelubricating oil may be a synthetic lubricating oil. Suitable syntheticlubricating oil include, for example, synthetic ester lubricating oils,which oils include diesters such as di-octyl adipate, di-octyl sebactateand tri-decyl adipate; or polymeric hydrocarbon lubricating oils such asliquid polyisobutylene and poly alpha olefins. Often, a mineral oil isemployed in this capacity.

Another class of lubricating oils suitable for purposes of thisinvention is hydrocracked oils, where the refining process furtherbreaks down the middle- and heavy-distillate fractions in the presenceof hydrogen at high temperature and moderate pressures. Hydrocarckedoils typically have kinematic viscosity at 100° C. of from 2 to 40, forexample, from 3 to 15 mm² s⁻¹ and a viscosity index in the range of from100 to 110, for example, from 105 to 108.

The term “brightstock” is used by persons skilled in the art to refer tobase oils that are solvent-extracted, de-asphalted products from vacuumresiduum. They generally have a kinematic viscosity at 100° C. of from28 to 36 mm² s⁻¹, and are typically used in proportion of less than 50,such as less than 40, more preferably less than 35 wt. %, based on thetotal weight of the lubricating oil composition. An exemplary dieselcylinder lubricant composition of the present invention comprised anESSO™ Core 2500 Base Oil that is a brightstock in an amount of about 35wt. %, as part of a mixture with another non-brightstock base oil.

The diesel cylinder lubricant composition of the present inventionincludes a major amount of an oil of lubricating viscosity. By “a majoramount” it is meant that the diesel cylinder lubricant compositionsuitably includes at least about 40 wt. %, preferably at least about 50wt. %, more preferably at least about 60 wt. %, and particularlypreferably, at least about 70 wt. %, of an oil of lubricating viscosityas described above, based on the total weight of the diesel cylinderlubricant oil composition.

3. Overbased Metal Detergents

The diesel engine cylinder lubricant of the present invention mayfurther comprise one or more overbased metal detergents. An overbasedmetal detergent molecule typically comprises a surfactant part and ametal part. The surfactant part of the overbased metal compoundpreferably contains at least one hydrocarbyl group, for example, as asubstituent on an aromatic ring. An example of substituted aromatic ringis a phenol group. The term “hydrocarbyl” as used herein means that thegroup concerned is primarily composed of hydrogen and carbon atoms andis bonded to the remainder of the molecule via a carbon atom, but doesnot exclude the presence of other atoms or groups in a proportioninsufficient to detract from the substantially hydrocarboncharacteristics of the group. Advantageously, the one or morehydrocarbyl groups in the surfactant part of the metal detergent of thepresent invention are aliphatic groups, preferably alkyl or alkylenegroups, especially alkyl groups, which may in turn be linear orbranched. The total number of carbon atoms in hydrocarbyl groups in thesurfactant part of a suitable overbased metal detergent is at leastsufficient to impart the desired oil-solubility to the detergent.

Phenols and/or their phenate salts, from which exemplary overbased metaldetergents of the present invention may derive, may be non-sulfurized orsulfurized, but are preferably sulfurized. Further, the term “phenol” asused herein includes phenols that contain more than one hydroxyl group(e.g., alkyl catechols) or fused aromatic rings (e.g., alkyl naphthols);or phenols that have been modified by chemical reactions. Suchchemically modified phenols may include, for example, alkylene-bridgedphenols; Mannich base condensed phenols; and saligenin-type phenylsproduced by a reaction of a phenol and an aldehyde under basicconditions. Preferred phenols may be derived from the formula:

wherein R represents a hydrocarbyl group and y represents 1 to 4. Wherey is greater than 1, the hydrocarbyl groups may be the same ordifferent.

In their oft-used sulfurized forms, sulfurized hydrocarbyl phenols maybe represented by the formula:

wherein x is generally from 1 to 4. In some cases, more than two phenolmolecules may be linked by Sx bridges. In both the formulae above, thehydrocarbyl groups represented by R are advantageously alkyl groups,which may contain 5 to 100, preferably 5 to 40, especially 9 to 12,carbon atoms, with the average number of carbon atoms in all of the Rgroup being at least 9 in order to ensure adequate solubility in oil.Preferred alkyl groups are nonyl(tripropylene) groups.Hydrocarbyl-substituted phenols are often also referred to as “alkylphenols.”

Methods of sulfurizing phenols or phenate are known to those skilled inthe art. Specifically, a sulfurizing agent, which introduces the-(Sx)-bridging group, should be used, wherein x is generally from 1 toabout 4. Accordingly the reaction may be conducted with elemental sulfuror a halide thereof. If elemental sulfur is used, the sulfurizationreaction may take place after the alkyl phenol compound is heated atfrom 50 to 250, preferably above 100° C. If a sulfur halide is used, thesulfurization reaction may take place after the alkyl phenol is treatedat from −10 to 120, preferably above 60° C. These reactions aretypically conducted in the presence of a suitable diluent, which mayadvantageously comprise a substantially inert organic diluent such as amineral oil or an alkane. Moreover, where elemental sulfur is used asthe sulfurizing agent, it may be desirable to use a basic catalyst suchas sodium hydroxide; or an organic amine, preferably a heterocyclicamine such as morpholine.

As indicated above, the term “phenol” as used herein includes phenolsthat have been modified by chemical reaction with, for example, analdehyde, and Mannich base-condensed phenols. Aldehydes with whichphenols may be modified include, for example, formaldehyde,propionaldehyde and butyraldehyde. The preferred aldehyde isformaldehyde. Various aldehyde-modified phenols are described in, forexample, U.S. Pat. No. 5,259,967, the disclosures of which, to theextent they are relevant to aldehyde-modification of phenol and to theextent they do not conflict with the disclosures and claims herein, areincorporated by reference. Mannich base-condensed phenols are preparedby the reaction of a phenol, an aldehyde and an amine. Examples ofsuitable Mannich base-condensed phenols are described in, for example,GB-A-2 121 432, the disclosures of which, to the extent they arerelevant to Mannich-base-condensed phenols, and to the extent they donot conflict with the disclosures and claims herein, are incorporated byreference. In general, the phenols may further include substituentsother than those mentioned above, provided that such substituents do notdetract significantly from the surfactant properties of the phenols.Examples of such substituents include methoxy groups and halogen atoms.

Suitable detergents may also originate from salicylic acids. Salicylicacids used in accordance with the invention may be non-sulfurized orsulfurized, and may be chemically modified and/or contain additionalsubstituents such as, for example, those discussed above for phenols. Inalkyl-substituted salicylic acids, the alkyl groups advantageouslycontain 5 to 100, preferably 9 to 30, especially 14 to 20, carbon atoms.Processes similar to those described above may also be used to sulfurizea hydrocarbyl-substituted salicylic acid. Salicylic acids are typicallyprepared by the carboxylation, by the Kolbe-Schmitt process, ofphenoxides, and in that instance, are generally obtained in admixturewith uncarboxylated phenol.

Other suitable detergents may originate from sulfonic acids, which aretypically obtained by sulfonation of hydrocarbyl-substituted, especiallyalkyl-substituted, aromatic hydrocarbons, for example, those obtainedfrom the fractionation of petroleum by distillation and/or extraction,or by the alkylation of aromatic hydrocarbons. Suitable sulfonic acidsinclude those obtained by alkylating benzene, toluene, xylene,naphthalene, biphenyl or their halogen derivatives, such as, forexample, chlorobenzene, chlorotoluene, or chloronaphthalene. Alkylationof aromatic hydrocarbons may be carried out in the presence of acatalyst with alkylating agents having from 3 to more than 100 carbonatoms, such as, for example, haloparaffins; olefins that may be obtainedby dehydrogenation of paraffins; and polyolefins such as polymers ofethylene, propylene, butene and the like. These alkylaryl sulphonicacids typically contain from 7 to 100 or more carbon atoms. Theypreferably contain from 16 to 80, or 12 to 40, carbon atoms peralkyl-substituted aromatic moiety, depending on the source from whichthey are obtained. These suitable sulfonic acids are neutralized toprovide sulfonates, which process is effectuated optionally in thepresence of hydrocarbon solvents and/or diluent oils, as well aspromoters and viscosity control agents.

Sulfonic acids from which the metal detergents of the present inventionmay derive may further include alkyl sulfonic acids and alkenyl sulfonicacids. In such compounds the alkyl group and/or alkenyl group suitablycontain 9 to 100, advantageously 12 to 80, especially 16 to 60, carbonatoms.

Yet another type of suitable metal detergents may be derived fromcarboxylic acids, which typically include mono- and/or dicarboxylicacids. Preferred monocarboxylic acids are those containing 1 to 30,especially 8 to 24, carbon atoms. Examples of monocarboxylic acids areiso-octanoic acid, stearic acid, oleic acid, palmitic acid and behenicacid. An example of a suitable so-octanoic acid may be the mixture of C₈acid isomers as sold by Exxon Chemicals under the trade name CEKANOIC™.Other suitable carboxylic acids are those with tertiary substitutions atthe α-carbon atom and dicarboxylic acids with more than 2 carbon atomsseparating the carboxylic groups. Further, dicarboxylic acids with morethan 35, for example, 36 to 100, carbon atoms are also suitable.Unsaturated carboxylic acids can optionally be sulfurized. Just assalicylic acids are not classified as phenol detergents herein despitethe presence of a hydroxyl group on the aromatic ring, salicylic acidsare not regarded as carboxylic acid detergents although they contain acarboxylic group.

Examples of other detergents that may be used in accordance with theinvention include the following compounds, and derivatives thereof:naphthenic acids, especially naphthenic acids containing one or morealkyl groups; dialkylphosphoric acids; dialkylthiophosphonic acids; anddialkyldithiophosphoric acids; high molecular weight, and preferablyethoxylated, alcohols; dithiocarbamic acids; and thiophosphines.Examples also include optionally sulfurized alkaline earth metalhydrocarbyl phenates that have been modified by carboxylic acids such asstearic acid, for examples as described in EP-A-271 262; and phenolatesas described in EP-A-750 659. The disclosures in these patents, to theextent they do pertain to the modified and optionally sulfurizedhydrocarbyl phenates, and to the extent they do not conflict with thedisclosures and claims herein, are incorporated by reference.

The detergents discussed above are suitably overbased, which helps toneutralize the sulfonic acid that is inevitably produced in thecombustion exhaust when diesel fuels containing sulfur, regardless itslevel, are used to drive these engines. Suitable overbased metalcompounds include alkali metal and alkaline earth metal additives suchas overbased oil-soluble or oil-dispersible calcium, magnesium, sodium,or barium, salts of a surfactant selected from phenol, sulfonic acid,carboxylic acid, salicylic acid, and naphthenic acid. The overbasing istypically provided by an oil-soluble salt of the metal, for example, acarbonate, a basic carbonate, an acetate, a formate, a hydroxide, or anoxalate, which is stabilized by the oil-soluble salt of the surfactant.Preferably the metal, whether the metal of the oil-soluble oroil-dispersible salt, is calcium.

Also suitable for use in the present invention are overbased metaldetergents, preferably overbased calcium detergents, that contain atleast two surfactant groups, such as phenol, sulfonic acid, carboxylicacid, salicylic acid and naphthenic acid, which may be obtained bymanufacture of a hybrid material in which two or more differentsurfactant groups are incorporated during the overbasing process. Thehybrid material can also be obtained by simply physically mixing two ormore overbased detergents of different types. Examples of hybridmaterials include an overbased calcium salt of surfactants phenol andsulfonic acid; an overbased calcium salt of surfactants phenol andcarboxylic acid; an overbased calcium salt of surfactants phenol,sulfonic acid and salicylic acid; and an overbased calcium salt ofsurfactants phenol and salicylic acid.

In instances where at least two overbased metal compounds are present,any suitable proportions by mass may be used, preferably the mass tomass proportion of any one overbased metal compound to any other metaloverbased compound is in the range of from 5:95 to 95:5, such as from90:10 to 10:90, more preferably from 20:80 to 80:20, advantageously from70:30 to 30:70. Persons skilled in the art have known and describedlubricant oil compositions comprising hybrid overbased detergents in,for example, WO-A-97/46643; WO-A-97/46644; WO-A-97/46645; WO-A-97/46646;and WO-A-97/46647.

The term “an overbased calcium salt of surfactant” refers to anoverbased detergent in which the metal cations of the oil-insolublemetal salt are essentially calcium cations. Small amounts of othercations may be present, but typically at least 80, more typically atleast 90, such as at least 95, %, of the cations in the oil-insolublemetal salt, are calcium ions.

The levels of overbasing in the metal detergents of the presentinvention may vary widely, but preferably the TBN of each of theoverbased metal detergents is at least 100, or at least 150, or at least200, such as up to 500. An exemplary diesel cylinder lubricant of thepresent invention comprises a highly overbased calcium sulfonatedetergent having a TBN of about 430.

Typically, the amount of one or more overbased metal detergents in thelubricant is at least 0.5, particularly in the range of from 0.5 to 30,such as from 3 to 25, or 2 to 20, or 5 to 22, wt. %, based on totalweight of the lubricant oil. An exemplary diesel cylinder lubricant ofthe present invention comprises about 16 wt. % of a highly overbasedsulfonate detergent. At least 90%, more preferably at least 95%, such asat least 98%, of the TBN of the lubricating oil composition of thepresent invention is provided for by the one or more overbasedmetal-containing detergents.

The overbased metal compounds of the present invention may also beborated. In that case, the boron-contributing compound, such as themetal borate, is considered to form part of the overbasing.

4. Foam Inhibitors

Foam forms when a large amount of gas is entrained in a liquid. Whilefoaming is desirable in certain applications, such as floatation,washing and cleaning, it is undesirable in others. In lubricant-relatedapplications, foaming can be an impediment because it leads toineffective lubrication. Over time, it may also cause oxidativedegradation of the lubricant. The viscosity and surface tension of alubricant determine the stability of the foam. Low-viscosity oilsproduce foams with large bubbles, which tend to break quickly and beminimally problematic. But high-viscosity oils, such as those used inthe diesel cylinder lubricants of the present invention, generate stablefoams that contain fine bubbles and are difficult to break. The presenceof surface-active materials, such as for example, the surfactantmaterials of the present invention, detergents, and/or dispersants,further increases the lubricant's tendency to foam.

Foam inhibitors control foam formation by altering the surface tensionof the oil and by facilitating the separation of the air bubbles fromthe oil phase. In general, these additives have limited solubility inoil, thus they are typically added as fine dispersions. Silicones (e.g.,polysiloxanes), polyalkyl acrylates, and polyalkyl metacrylates are foaminhibitors that can be suitably used in the diesel cylinder lubricantsof the present invention, with silicones being more preferred. Anexemplary diesel cylinder lubricant of the present invention comprisesabout 0.06 wt. % of a silicon-based foam inhibitor.

5. Other Additives

The diesel cylinder lubricant of the present invention may include asco-additives one or more other wear inhibitors, as well as various othermaterials. Such other materials include, for example, antioxidants,antifoaming agents, and/or rust inhibitors. Further details of exemplaryco-additives are described below:

A. Zinc-Containing Wear Inhibitor

Depending upon the type of application used, the diesel cylinderlubricating oil composition can further comprise from about 0.1 wt. % toabout 2 wt. % of at least one zinc dithiophosphate wear-inhibitionadditive. That zinc dithiophosphate wear-inhibition additive isparticularly useful in ships, workboats and stand-by or continuouselectrical power generation, where the additive may be a zincdialkyldithiophosphate derived from primary alcohols.

For marine applications, a particular physical mixture of zincdialkyl-dithiophosphates may be preferred because it increases the watertolerance of diesel engines that are susceptible to water contamination.That physical mixture may have from about 20 wt. % to about 90 wt. %,preferably from about 40 wt. % to about 80 wt. % of a zincdialkyl-dithiophosphate derived from only primary alkyl alcohols, andfrom about 10 wt. % to about 80 wt. %, preferably from about 20 wt. % toabout 60 wt. %, of a zinc dialkyl-dithiophosphate derived from onlysecondary alkyl alcohols. This physical mixture of zincdialkyl-dithiophosphates differs from chemical mixtures of zincdialkyl-dithiophosphates derived from mixtures of different types ofalcohols.

The individual zinc dialkyldithiophosphates can be produced fromdialkyldithiophosphoric acids of the formula:

The hydroxy alkyl compounds from which the dialkyldithiophosphoric acidsare derived can be represented generically by the formula ROH or R′OH,where R or R′ is alkyl or substituted alkyl group. Preferably, R or R′is a branched or non-branched alkyl containing about 3 to about 20, ormore preferably, about 3 to about 8, carbon atoms.

Individual dialkyldithiophosphoric acids can also be produced fromhydroxy alkyl compounds. As is recognized in the art, these hydroxyalkyl compounds need not be monohydroxy alkyl compounds. That is, thedialkyldithiophosphoric acids may be prepared from mono-, di-, tri-,tetra-, and other polyhydroxy alkyl compounds, or mixtures of two ormore of the foregoing. Most commercially available alcohols can be usedfor this purpose because they are typically not pure compounds but aremixtures containing a predominant amount of the desired alcohol andminor amounts of various isomers and/or longer- or shorter-chainalcohols.

Preferably, a zinc dialkyldithiophosphate derived from only primaryalkyl alcohols is derived from a single primary alcohol. Preferably,that single primary alcohol is 2-ethylhexanol. Preferably, a zincdialkyldithiophosphate derived from only secondary alkyl alcohols isderived from a mixture of secondary alcohols. Preferably, that mixtureof secondary alcohols is a mixture of 2-butanol and 4-methyl-2-pentanol.The phosphorus pentasulfide reactant used in the dialkyldithiophosphoricacid formation step of this invention may also contain minor amounts ofany one or more of P₂S₃, P₄S₃, P₄S₇, or P₄S₉. Such phosphorus sulfidecompositions may contain minor amounts of free sulfur. It should benoted that, while the structure of phosphorus pentasulfide is generallyrepresented as P₂S₅, the actual structure is believed to contain fourphosphorus atoms and ten sulfur atoms, i.e., P₄S₁₀. For the purposes ofthis invention, the phosphorus sulfide reactant will be considered as acompound having the structure of P₂S₅ with the understanding that theactual structure is probably P₄S₁₀.

B. Oxidation Inhibitors

Oxidation inhibitors, or antioxidants, reduce the tendency of mineraloils to deteriorate in service, evidence of such deterioration being,for example, the production of varnish-like deposits on metal surfacesand of sludge, and viscosity increase. Suitable oxidation inhibitorsinclude, for example, sulfurized alkyl phenols and alkali or alkalineearth metal salts thereof; diphenylamines; phenyl-nehthylamines; andphosphosulfurized or sulfurized hydrocarbons. Other oxidation inhibitorsor antioxidants include various oil-soluble copper compounds. The coppermay, for example, be in the form of a copper dihydrocarbyl thio- ordithio-phosphate. Alternatively, the copper may be added as the coppersalt of a synthetic or natural carboxylic acid such as, for example, aC₈ to C₁₈ fatty acid, an unsaturated acid, or a branched carboxylicacid. Also useful are oil-soluble copper dithiocarbamates, sulfonates,phenates, and acethylacetonates. Examples of particular useful coppercompounds include basic, neutral, or acidic copper Cu I and/or Cu IIsalts derived from alkenyl succinic acids or anhydrides.

C. Ashless Dispersants

Dispersants are additives that suspend oil-insoluble resinous oxidationproducts and particulate contaminants in the bulk oil. Persons skilledin the art often add various dispersants to lubricating oils to minimizesludge formation, particulate-related abrasive wear, viscosity increase,and oxidation-related deposit formation.

It is known that dispersants perform these functions via one or moremeans selected from: (1) solubilizing polar contaminants in theirmicelles; (2) stabilizing colloidal dispersions in order to preventaggregation of their particles and their separation out of oil; (3)suspending such products, if they form, in the bulk lubricant; (4)modifying soot to minimize its aggregation and oil thickening; and (5)lowering surface/interfacial energy of undesirable materials to decreasetheir tendency to adhere to surfaces. The undesirable materials aretypically formed as a result of oxidative degradation of the lubricant,the reaction of chemically reactive species such as carboxylic acidswith the metal surfaces in the engine, or the decomposition of thermallyunstable lubricant additives such as, for example, extreme pressureagents.

In diesel-fueled engines such as the 2-stroke diesel engines of thepresent invention, soot from the combustion chamber is the key componentof carbon and lacquer deposits that occur on pistons, and sludge. Thesedeposits result when soot combines with resin. In general, lacquer isrich in resin and carbon is rich in soot. Sludge results when sootcombines with oxygenated species, oil, and water. Local pistontemperatures and the lubricant's ash-producing tendency have alsoprofound effects on the composition of the carbon deposits. Dispersantssuppress the interaction between resin and soot particles, bypreferentially associating with them and, at the same time, keeping themsuspended in the bulk lubricant. Since both resin and soot particles arepolar in character, either by their very nature or due to adsorbed polarimpurities, the dispersant associates with these particles via its polarend.

A typically dispersant molecule comprises three distinct structuralfeatures: (1) a hydrocarbyl group; (2) a polar group; and (3) aconnecting group or a link. The hydrocarbyl group is typically polymericin nature, and may have a molecular weight of at or above about 2000Daltons, preferably at or above about 3000 Daltons, more preferably ator above about 5000 Daltons, and even more preferably at or above about8000 Daltons. A variety of olefins, such as polyisobutylene,polypropylene, polyalphaolefins, and mixtures thereof, can be used tomake suitable polymeric dispersants. Among suitable polymericdispersants, polyisobutylene-derived dispersants are the most common.Typically the number average molecular weight of polyisobutylene inthose dispersants ranges between about 500 and about 3000 Daltons, or,in some embodiments, between about 800 to about 2000 Daltons, or infurther embodiments, between about 1000 to about 2000 Daltons. Molecularweight distribution and the length and degree of branching are, like thenumber average molecular weight of the polyisobutylenes, important tothe effectiveness as a dispersant. In a given dispersant, the polargroup is usually nitrogen- or oxygen-derived. Nitrogen-based dispersantsare typically derived from amines. The amines from which thenitrogen-based dispersants are derived are often polyalkylenepolyamines,such as, for example, diethylenetriamine and trethylenetetramine.Amine-derived dispersants are also called nitrogen- oramine-dispersants, while those derived from alcohol are also calledoxygen or ester dispersants. Oxygen-based dispersants are typicallyneutral while the amine-based dispersants are typically basic. Chemicalclasses suitable for use as dispersants include alkenylsuccinimides,alkenyl succininate esters, high molecular weight amines, Mannich bases,and phosphonic acid derivatives. Polyisobutenyl succinic acidderivatives such as succinimides and succinate esters are commerciallythe most commonly used dispersant types.

Lubricating oil compositions of the present invention may comprise anamount of an ashless dispersant that is sufficient to measurably reducethe amount of soot deposits on the cylinders and/or sludge formation. By“measurably reduce” it is meant that the reduction can be measured bystandard testing methods such as, for example, the ASTM Sequence VE/VGTest and Caterpillar IK, 1M-PC, IN, IP, and IR tests. It typicallyrefers to a level of reduction that is at least 2%, or at least 5%, ormore preferably, at least 10% of the level prior to treatment by thedispersants. Suitable diesel cylinder lubricating oil compositions ofthe present invention comprise about 0.1 to about 5 wt. %, such as about0.2 to about 2 wt. %, or about 0.5 to about 1 wt. % of one or moreashless dispersants.

D. Rust Inhibitors

Marine diesel engines, as their names suggest, operate in omnipresenceor near omnipresence of sea water, which typically contains largeamounts of various salts. Stationary large diesel engines in powerplants also operate in the presence of water. Rust forms when anelectrochemical corrosive reaction takes place in the presence ofelectrolytes such as, for example, water, acids, alkalis, and salts.Electrochemical corrosion or the rusting process involves the reactionof metals in the presence of electrically conducting solutions, orelectrolytes, and occurs in two stages: (1) the anodic process and thecathodic process. In the anodic process, metal goes into solution asions with extra electrons left over. The process is also often regardedas an oxidation process. The cathodic process involves the reaction ofthus generated electrons with water and oxygen to form the hydroxideions. This process is also often considered a reduction process. Insolution, the metal ions then combine with hydroxide ions to form metalhydroxide, or hydrated oxides. The speed of electrochemical corrosiondepends upon the nature of the metal oxide film, the presence or absenceof polar solvent such as water, the presence or absence of anelectrolyte (salts, acids or bases), and the temperature.

Protection against rust is an important consideration in formulatinglubricants for marine diesel engines for the obvious reason that theenvironments in which such engines operate are rife with the elementsthat can lead to rust. Such protection is likewise important forstationary operations of 2-stroke engines. Without protection, rustultimately causes a loss of metal, thereby lowering the integrity of theequipment, and resulting in engine malfunction. In addition, corrosionexposes fresh metal that can wear at an accelerated rate, perpetuated bythe metal ions that have been released into the fluid and are now actingas oxidation promoters.

For protection, rust inhibitors are used. They attach themselves tometal surfaces to form an impenetrable protective film, which can bephysically or chemically adsorbed to the surface. Specifically, filmformation occurs when the additives interact with the metal surface viatheir polar ends and associate with the lubricant via their nonpolarends, in a manner similar to that of friction modifiers. Suitable rustinhibitors may include, for example, various nonionic polyoxyethylenesurface active agents such as polyoxyethylene lauryl ether,polyoxyethylene higher alcohol ether, polyoxyethylene nonylphenyl ether,polyoxyethylene octylphenyl ether, polyoxyethylene octyl stearyl ether,polyoxyethylene oleyl ether, polyoxyethylene sorbitol monostearate,polyoxyethylene sorbitol mono-oleate, and polyethylene glycolmonoolcate. Suitable rust inhibitors may further include other compoundssuch as, for example, stearic acid and other fatty acids, dicarboxylicacids, metal soaps, fatty acid amine salts, metal salts of heavysulfonic acid, partial carboxylic acid ester of polyhydric alcohol, andphosphoric ester.

E. Demulsifiers

In the presence of water, lubricant oil compositions taken on anincreased tendency to form emulsions. The diesel cylinder lubricants ofthe present invention are used to lubricate marine diesel engines orstationary diesel engines that operate in environments where watercontamination is often an unavoidable problem. To combat the operationaldrawbacks associated with the formation of excess emulsions,demulsifiers are added to such formulations to enhance water separationand suppress foam formation. Typically, most demulsifiers are oligomersor polymers with a molecular weight of up to about 100,000 Daltons andcontain about 5 to about 50% polyethylene oxide in a combined form.Commonly used demulsifiers include block copolymers of propylene oxideor ethylene oxide and initiators, such as, for example, glycerol,phenol, formaldehyde resins, soloxanes, polyamines, and polyols. Toprevent common water-in-oil emulsions, polymers containing about 20 toabout 50% ethylene oxide are suitable. These materials concentrate atthe water-oil interface and create low viscosity zones, therebypromoting droplet coalescence and gravity-driven phase separation. Lowmolecular weight materials, such as, for example, alkali metal oralkaline earth metal salts of dialkylnaphthalene sulfonic acids, arealso useful in certain applications.

F. Antiwear and/or Extreme Pressure Agents

Wear occurs in all equipment that has moving parts in contact.Specifically, three conditions commonly lead to wear in diesel engines:(1) surface-to-surface contact; (2) surface contact with foreign matter;and (3) erosion due to corrosive materials. Wear resulting fromsurface-to-surface contact is friction or adhesive wear, from contactwith foreign matter is abrasive wear, and from contact with corrosivematerials is corrosive wear. Fatigue wear is an additional type of wearthat is common in equipment where surfaces are not only in contact butalso experience repeated stresses for prolonged periods. Abrasive wearcan be prevented by installing an efficient filtration mechanism toremove the offending debris. Corrosive wear can be addressed by usingadditives such as those described above, which neutralize the reactivespecies that would otherwise attack the metal surfaces. The control ofadhesive wear requires the use of additives called antiwear andextreme-pressure (EP) agents.

Under optimal conditions of speed and load, the metal surfaces of theequipment should be effectively separated by a lubricant film.Increasing load, decreasing speed, or otherwise deviating from suchoptimal conditions promote metal-to-metal contact. This contacttypically causes a temperature increase in the contact zone due tofrictional heat, which in turn leads to the loss of lubricant viscosityand hence its film-forming ability. Antiwear additive and EP agentsoffer protection by a similar mechanism, although EP additives typicallyrequire higher activation temperatures and load than antiwear additives.

Antiwear and/or EP additives function by thermal decomposition and byforming products that react with the metal surface to form a solidprotective layer. This solid metal film fills the surface asperities andfacilitates effective film formation, thereby reducing friction andpreventing welding and surface wear.

Most antiwear and extreme pressure agents contain sulfur, chlorine,phosphorus, boron, or combinations thereof. The classes of compoundsthat inhibit adhesive wear include, for example, alkyl and aryldisulfides and polysulfides; dithiocarbamates; chlorinated hydrocarbons;and phosphorus compounds such as alkyl phosphites, phosphates,dithiophosphates, and alkenylphosphonates.

Various commonly used antiwear agents can be included in the dieselcylinder lubricant oil compositions of the present invention. Forexample, zinc salts of dithiohosphoric acids, in addition to providingantiwear protection, offer additional benefits as oxidation andcorrosion inhibitors. These salts may include, for example, zinc dialkyldithiophosphates and zinc diaryl dithiophosphates. Methods of makingzinc-salts suitable for this purpose are known in the art. Moreover,alkyl and aryl disulfides and polysulfides, dithiocarbamates,chlorinated hydrocarbons, dialkyl hydrogen phosphites, and salts ofalkyl phosphoric acids can also be suitable EP agents. Methods of makingthese EP agents are known in the art. For example, polyulfides aresynthesized from olefins either by reacting with sulfur or sulfurhalides, followed by dehydrohalogenation. Dialkydithiocarbamates areprepared either by neutralizing dithiocarbamic acid (which can beprepared by reacting a diakylamine and carbon disulfide at lowtemperature) with bases, such as zinc oxide or antimony oxided, or byits addition to activated olefins, such as alkyl acrylates.

One or more EP agents may be used for purpose of the present invention.Specifically, the use of more than one EP agents may lead to synergism.For example, synergism may be observed between sulfur andchlorine-containing EP agents. An exemplary diesel cylinder lubricant ofthe present invention may include as an EP agent one or more materialsselected from: zinc dialkyldithiophosphate (primary alkyl type &secondary alkyl type), sulfurized oils, diphenyl sulfide, methyltrichlorostearate, chlorinated naphthalene, fluoroalkylpolysiloxane, andlead naphthenate.

G. Friction Modifiers

Friction modifiers are agents that modify the frictional properties of alubricant. They are typically long-chain molecules with a polar endgroup and a nonpolar linear hydrocarbon chain. The polar end groupseither physically adsorb onto the metal surface or chemically react withit, while the hydrocarbon chain extend into the lubricant. The chainsassociated with one another and the lubricant to form a strong lubricantfilm.

Suitable friction modifiers may include, for example, fatty alcohols,fatty acids, fatty amides, and molybdenum compounds. For the fattyalcohol and fatty acid families of compounds, friction-modifyingproperties are a function of the length and the structure of thehydrocarbon chain and the nature of the functional group. Long andlinear chain materials reduce friction more effectively than short andbranched chain materials. Also, fatty acids are typically betterfriction modifiers than fatty amides, which in turn are better thanfatty alcohols. Saturated acids, containing a 13 to 18 carbon chains,are generally preferred. Lower molecular weight fatty acids are avoidedbecause of their corrosivity. Fatty acid derivatives are also among themost commonly used friction modifiers. Exemplary diesel cylinderlubricants of the present invention may comprise as friction modifiersone or more materials selected from: fatty alcohols, fatty acids,amines, and borated or other esters.

H. Multi-Functional Additives

Various additives mentioned or not mentioned herein can provide amultiplicity of effects to the diesel cylinder lubricant oil compositionof the present invention. Thus, for example, a single additive may actas a dispersant as well as an oxidative inhibitor. Indeed, thecorrosive-wear inhibiting and/or reducing surfactant materials of thepresent invention may serve as multi-functional additives, providing thelubricant oil compositions with capacities to reduce and/or inhibitcorrosive wear on the power cylinders as well as dispersancy.Multi-functional additives are well known in the art. Other suitablemulti-functional additives may include, for example, sulfurizedoxymolybdenum dithiocarbamate, sulfurized oxymolybdenum organo phosphorodithioate, oxymolybdenun monoglyceride, amine-molybdenum complexcompound, and sulfur-containing molybdenym complex compounds.

I. Pour Point Depressants

The pour point is the lowest temperature at which an oil will pour whencooled under defined conditions. In general, the pour point isindicative of the amount of straight-chain paraffins in an oil. At lowtemperature, straight-chain paraffins tend to separate as crystals witha lattice type structure. These crystals can trap a substantial amountof oil via association, inhibit oil flow, and ultimately hinder properlubrication of the equipment. Although base oil suppliers make an effortto remove most of the straight-chain paraffins, complete removal ofthose molecules is often not practical due to process limitations andeconomics. Also, these molecules may offer beneficial viscositycharacteristics. Thus, for operations at low temperatures, personsskilled in the art typically favor incomplete removal of straight-chainparaffin molecules in combination with the use of pour point depressantsin the lubricant oils.

Pour point depressants generally possess one or more structural featuresselected from: (1) polymeric structure; (2) waxy and non-waxycomponents; (3) comb structure comprising a short backbone with longpendant groups; and (4) broad molecular weight distribution. Manypolymeric pour point depressants are known in the art and some arecommercially available. Most commercial pour point depressants areorganic polymers, although some nonpolymeric materials have also beenshown to be effective, including, for example, tetra (long-chain) alkylsilicates, phenyltrstearyloxysilane, and pentaerythritol tetrastearate.Examples of suitable pour point depressants include alkylatednaphthalenes, poly(alkyl methacrylates), poly(alkyl fumarates), styreneesters, oligomerized alkyl phenols, phthalic acid esters, ethylene-vinylacetate copolymers, and other mixed hydrocarbon polymers. Pour pointdepressants are typically used at treatment levels at or below about 1wt. %.

6. 2-Cycle Diesel Engine Cylinder Lubricating Oil Composition

The present invention pertains to a lubricating oil composition suitablefor use in a slow- or medium-speed diesel engine that operates on the2-stroke cycle. This lubricating oil composition comprises:

(a) a major amount of a base oil of lubricating viscosity;

(b) one or more of oil-soluble surfactant materials as described above,in a combined amount sufficient to substantially reduce the corrosivewear on the power cylinders of the 2-stroke diesel engines;

(c) one or more overbased metal detergents in a combined amountsufficient to give the lubricant oil composition a total TBN of about 5to 100, preferably of about 30 to about 50, or of about 60 to 80; and

(d) a minor amount of one or more foam inhibitors.

The term “substantially reduce” refers to a reduction of at least about5%, preferably at least about 10%, more preferably at least about 15%,as compared to the amount of measurable corrosive wear on the powercylinders when they are lubricated by a comparative compositioncontaining no surfactant material of the present invention.

That diesel cylinder lubricant oil composition can further compriseother additives as exemplified and described herein.

In a further embodiment, a diesel cylinder lubricant oil composition isproduced by blending a mixture of the above components. The lubricatingoil composition produced by that method may have a slightly differentcomposition than the initial mixture, because the components mayinteract with each other. The components can be blended in any order andcan be blended as combinations of components.

Lubricating the power cylinders of 2-stroke diesel engines with thelubricating oil compositions of the present invention can provideenhanced protection to these cylinders against corrosive wear. Thelubricating oil compositions of the present invention may also includeone or more other additives such as, for example, a high TBN metaldetergent, which provides certain baseline level of protection againstcorrosive wear. If so, then the protective effect of the surfactantmaterials of the present invention is above and beyond the protectiveeffects provided by the additional, high TBN, corrosive-wear controllingadditives,

7. Additive Concentrates

Additive concentrates are also within the scope of the presentinvention. The concentrates of this invention comprise the surfactantmaterials described above, preferably with at least one overbased metaldetergent, at least one foam inhibitor, and at least one other additive,as disclosed above. The concentrates contain sufficient organic diluentto make them easy to handle during shipping and storage, especially whenthey are carried and blended onboard oceangoing vessels during longvoyages.

Suitably, from about 20 wt. % to about 80 wt. % of each concentrate isorganic diluent. Organic diluents that can be used include, for example,mineral oils or synthetic oils, just like those described above in the“Oil Of Lubricating Viscosity” section.

This invention will be further understood by reference to the followingexamples, which are not to be considered as limitative of its scope.

EXAMPLES

The following examples are provided to illustrate the present inventionwithout limiting it. While the present invention has been described withreference to specific embodiments, this application is intended toencompass those various changes and substitutions that may be made bythose skilled in the art without departing from the spirit and scope ofthe appended claims.

Example 1 A Low TBN Sulfonate Surfactant Improves Corrosive Wear Control

Various diesel cylinder lubricant oil samples were prepared. Theircapacities to control corrosive wear were measured in a Falex™ Pin andVee-Block Test. Specifically, the test was carried out in a standardFalex™ Pin and Vee-Block Lubricant Test Machine (Falex Corporation,Aurora, Ill.). The test was carried out in two phases: (1) a run-inphase; and (2) a test phase. During the run-in phase, a steel pin wasrotated between two steel Vee-blocks that were immersed in the oilsample to be tested. The Vee-blocks were pressed against the pin at apredetermined load of 445 Newtons for about 900 seconds. The test phasefollowed the run-in phase, where the oil temperature remained at 80° C.During the test phase, however, the Vee-blocks were pressed against thetest pin with a load of 1335 Newtons. A peristaltic pump having a tubewith an inner diameter of 0.5 mm was used to deliver sulfuric acid (at aconcentration of 3N in water) to the test pin, which was located about 1mm away from the opening of the tube, by spraying the acid onto the pin,at a flow rate of about 7.5 ml/hour. The test phase lasted about 7200seconds. The Vee-block used was a standard-coined Vee-Block with a 96±1°angle, made with AISI C-1137 steel (hardness: HRC 20-24, rms) (availablefrom Falex™ Corp.). The test pin used was a standard test pin, with a6.35 mm outside diameter and 31.75 mm length, made with AISI 3135 steel(hardness HRB 87-91, rms) (also available from Falex™ Corp.). The weightof the pin was measured before the test and after the completion of thetest phase. The weight loss was used to indicate the extent or level ofwear.

Each of Samples A and B comprised an oil of lubricating viscosity, anoil-soluble surfactant material, a highly overbased sulfonate detergent,and a foam inhibitor. Comparative Sample C comprised the same set ofcomponents as in Sample A or 1, except that Comparative Sample C did notcomprise either the 17 TBN sulfonate surfactant or the non-overbasedlinear alkyphenol surfactant. Components of these samples are listedbelow in Table 1.

The results of the Falex™ Pin and Vee-Block Test are also listed inTable 1. Accordingly, a diesel cylinder lubricant oil's capacity toresist corrosive wear was substantially improved as a result ofincluding a low TBN sulfonate surfactant. Moreover, such an improvementwas also apparent when the diesel cylinder lubricant oil comprised anon-overbased long-chain alkylphenol surfactant.

TABLE 1 Formulations A B C Additives: TBN 17 sulfonate surfactant  7.71wt. % C₁₈-C₂₈ Alkylphenol  6.90 wt. % surfactant TBN 430 SulfonateDetergent 16.04 wt. % 16.32 wt. % 16.32 wt. % Silicon-based foaminhibitor  0.06 wt. %  0.06 wt. %  0.06 wt. % TBN 70 70  70 Esso Core600 Base Oil 47.93 wt. % 39.32 wt. % 47.68 wt. % (600N) Esso Core 2500(150 28.26 wt. % 37.40 wt. % 35.94 wt. % Brightstock) Bench TestResults: Falex ™ Pin Weight Loss 20 79 186 (mg)

Example 2 Prophetic Example

Each of Samples D and E is prepared to comprise a major amount of an oilof lubricating viscosity, and a minor amount of a foam inhibitor.Samples D and E further comprise about 9.00 wt. % and about 9.30 wt. %of a 430 TBN calcium sulfonate detergent, respectively, bringing the TBNof each lubricating oil composition to about 40. Sample D comprisesabout 7.71 wt. % of a 17 TBN sulfonate surfactant. Sample E comprisesabout 6.90 wt. % of a non-overbased linear alkylphenol surfactant.

Comparative Sample F is prepared to comprise the same components asSample D or E, except that Comparative Sample F does not contain eitherthe 17 TBN sulfonate surfactant or the non-overbased linear alkyphenolsurfactant.

The pins in the Falex™ Pin and Vee-Block Test are measured for weightlosses. The pins tested in the presence of Sample Oils C and D areexpected to lose substantially less weight than the pins tested in thepresence of Comparative Sample F.

1. A marine cross-head two-stroke diesel cylinder lubricating oilcomposition comprising an admixture of: (a) a major amount of an oil oflubricating viscosity; (b) one or more high overbased metal-containingdetergents; (c) one or more foam inhibitors; and (d) one or morenon-overbased or low overbased oil-soluble surfactant materials toprovide enhanced corrosive wear control; wherein the marine cross-headtwo-stroke diesel cylinder lubricating oil composition has a TBN ofabout 5 to about 100, and further wherein the one or more non-overbasedor low overbased surfactant materials are present in an amount of about2 wt. % to about 25 wt. %.
 2. The lubricating oil composition of claim1, having a TBN of about 30 to about
 50. 3. The lubricating oilcomposition of claim 1, having a TBN of about 60 to about
 80. 4. Thelubricating oil composition of claim 1, wherein one of the one or moreoil-soluble surfactant materials is either a low TBN sulfonatesurfactant or a non-overbased sulfonate surfactant.
 5. The lubricatingoil composition of claim 4, wherein the low TBN sulfonate surfactant isa calcium sulfonate surfactant having a TBN of about 2 to about
 20. 6.The lubricating oil composition of claim 1, wherein one of the one ormore oil-soluble surfactant materials is a non-overbased linearalkylphenol surfactant.
 7. (canceled)
 8. The lubricating oil compositionof claim 7, wherein the one or more surfactants are present in an amountof about 4 wt. %, to about 20 wt. %.
 9. The lubricating oil compositionof claim 8, wherein the one or more surfactants are present in an amountof about 5 wt. % to about 15 wt. %.
 10. The lubricating oil compositionof claim 1, wherein at least 90% of the TBN of the lubricating oilcomposition is provided for by the one or more metal-containingdetergents.
 11. The lubricating oil composition of claim 10, wherein atleast 95% of the TBN of the lubricating oil composition is provided forby the one or more metal-containing detergents.
 12. The lubricating oilcomposition of claim 1, wherein one of the one or more metal-containingdetergents is a high-overbased calcium sulfonate detergent.
 13. Thelubricating oil composition of claim 1, wherein the amount of the one ormore metal-containing detergents is at least about 0.5 wt. %.
 14. Thelubricating oil composition of claim 13, wherein the amount of the oneor more metal-containing detergents is about 0.5 wt. % to about 30 wt.%.
 15. The lubricating oil composition of claim 14, wherein the amountof the one or more metal-containing detergents is about 3 wt. % to about25 wt. %.
 16. The lubricating oil composition of claim 15, wherein theamount of the one or more metal-containing, detergents is about 5 wt. %to about 22 wt. %.
 17. The lubricating oil composition of claim 1,wherein the one or more metal-containing detergents are hybrid overbasedmetal-containing detergents that are mixtures of at least two overbasedmetal-containing detergents.
 18. The lubricating oil composition ofclaim 1, further comprising one or more additives selected from: (1)zinc-containing wear inhibitors; (2) oxidation inhibitors; (3) rustinhibitors: (4) pour point depressants; (5) demulsifiers; (6) ashlessdispersants; (7) friction modifiers; (8) extreme-pressure agents; and(9) multi-functional additives.
 19. A method of providing enhancedcorrosive wear control on the cylinders of a 2-stroke diesel engine,comprising: (a) contacting at least some of the surfaces of thecylinders with the marine cross-head two-stroke diesel cylinderlubricating oil composition of claim 1; and (b) operating the 2-strokediesel engine in the presence of the marine cross-head two-stroke dieselcylinder lubricating oil composition.
 20. The method according to claim19, wherein the 2-stroke diesel engine is a slow-speed marine dieselengine or a medium-speed marine diesel engine.
 21. The method accordingto claim 19, wherein the lubricating oil composition further comprisesone or more additives selected from: (1) zinc-containing wearInhibitors; (2) oxidation inhibitors; (3) rust inhibitors; (4) pourpoint depressants; (5) demulsifiers; (6) ashless dispersants; (7)friction modifiers; (8) extreme-pressure agents; and (9)multi-functional additives.
 22. A method of making a marine cross-headtwo-stroke diesel cylinder lubricating oil composition comprisingblending the following components: (a) an oil of lubricating viscosity;(b) one or more high overbased metal-containing detergents; (c) one ormore foam inhibitors; and (d) one or more non-overbased or low overbasedoil-soluble surfactant materials to provide enhanced corrosive wearcontrol; wherein the TBN of the lubricating oil composition is fromabout 5 to about 100, and further wherein the one or more non-overbasedor low overbased surfactant materials are present in an amount of about2 wt. % to about 25 wt %.
 23. The method according: to claim 22, whereinthe TBN of the lubricating oil composition is either from about 30 toabout 50 or from, about 60 to about
 80. 24. The method according toclaim 22, wherein one or more additives selected from: (1)zinc-containing wear inhibitors; (2) oxidation inhibitors; (3) rustinhibitors; (4) pour point depressants; (5) demulsifiers; (6) ashlessdispersants; (7) friction modifiers; (8) extreme-pressure agents; and(9) multi-functional additives, are further blended into the lubricatingpit composition. 25.-28. (canceled)